In recent years, increased interest in sick house syndrome has brought about the development of a variety of techniques for efficiently removing major indoor air pollutants including particulates, mists, gases and volatile organic compounds (VOCs). However, these techniques are mostly focused on techniques employing photo-catalysts or ventilators. However, to date, no satisfactory method capable of efficiently removing indoor air pollutants has been introduced. In addition, of specific harmful substances that are released into the indoor air of domestic workplaces and new buildings, VOCs and formaldehyde are presumed to exceed acceptable concentration levels by 3 to 5 times. These harmful substances, which are continuously generated, are known to take at least one to two years to reach acceptable levels.
There are several methods for removing formaldehyde-containing indoor harmful substances, namely, oxidation/decomposition using photo-catalysts, adsorption using deodorizers or chemical solvents, and ventilation employing using ventilation systems. The oxidation/decomposition method using photo-catalysts is known to exhibit semi-permanent effects even after a single treatment. However, the oxidation/decomposition method has disadvantages of involving high process costs and taking a long time to degrade formaldehyde.
In addition, the adsorption method is disadvantageous in that chemical solvents or deodorizers must be directly used, and harmful substances and odors can be neutralized, but these effects are only temporary. Furthermore, the ventilation method induces a change of indoor air using a ventilation system, which suffers from the disadvantages of the difficulty of installing ventilation systems in apartments and high installation costs.
Meanwhile, in recent years, there has become known the ability of microorganisms to degrade VOCs including formaldehyde (referred to as  iodegradation? that are reported to be major indoor environmental contaminants and harmful to human body. Examples of these microorganisms include bacteria such as Pseudomonas putida, Rhodobacter sp., and Alcaligenes sp. and yeasts such as Hansenula sp.
These microorganisms are generally grown by using harmful substances as substrates necessary for development or degrading the harmful substances with enzymes created by the microorganisms. In particular, when formaldehyde is degraded using microorganisms, it is degraded by formaldehyde dehydrogenase to produce formate and carbon dioxide (CO2), which cause no air pollution and are harmless to human body.